Hi Adam,
I recently converted to a family account, there are only two of us now (kids have left home) but I decided it was worth it as our separate iCloud storage accounts were slowly growing for both of us and it seemed more sensible to pool our storage requirements in one account and only make one smaller payment a month.
I haven’t worked out yet if I need to cancel our old storage accounts and if I do so will all the documents in the old accounts be lost.
One the down side, I noticed that the first Time Machine backup, after the change, took forever, probably because the number of documents stored on the Mac had changed significantly as I turned on iCloud documents s I now had enough iCloud Drive space to do this. Also, this extended backup time repeated itself after I recently upgraded the Mac OS. Both times it required leaving the Mac on all night.
Of course, your experience may be different.
We don’t really use iTune much.
Good luck.
Paul Owen